The United States military currently requires vigorous testing for any piece of equipment that is intended for battle. In some instances, even the components of some equipment, such as mission critical equipment, must be individually tested.
Shock testing is one type of testing used by the military and military contractors. Shock testing is meant to simulate an attack, such as an explosion from a bomb, torpedo or missile that occurs in close proximity to the device or component. Electrical devices and components, such as circuit boards, sensors and routers, are often put through rigorous shock tests before the U.S. military will authorize their use in or for battle.
Shock testing helps ensure that mission critical components will not fail as a result of an explosion and/or other type of physical shock. These components are needed by military personal to continue to function properly during an attack. Accordingly, it is important that the shock testing of a component accurately simulate the type of shock(s) the component is likely to experience in battle.
Many U.S. Navy shock tests, for example, are currently administered by putting a device or component (sometimes referred to herein as a “shock test target” or “target”) on a barge or platform that is in water (such as a large lake or pond). The barge can be engineered to simulate the reverberation frequency or frequencies of a specific boat, ship or part of a ship, such as a ship's deck. Explosives are placed in the water under the barge, and ignited. The subsequent explosion creates a wave of energy and an air bubble, both of which can shock the target. Although different targets may have to meet different standards, many shock test targets pass a particular shock test if the target is not damaged too badly as a result of the shock and/or still functions properly after the shock.
The shock created by an explosion or other attack can be broken down into different phases. The first phase is the initial shock, which is caused by energy from an explosion and/or physical impact of, for example, a missile or bomb. That energy can travel as a shock wave. A bubble is also created when the initial shock is the result of an under water explosion. The bubble usually follows the path of the initial shock wave. Accordingly, both the initial shockwave and the bubble will impact physical media they encounter, and each can create shock waves that propagate through the media (such as the ship's deck). Subsequent shock waves are the result of the energy from the initial shock being distributed and reverberating through the media.
Different substances and combinations of substances will react to different types and magnitudes of shock waves. An explosion directed at the side of a surface ship, for example, is likely to also cause the ship to rock side to side, thereby creating rotational and athwartship forces, while many of its components (such as its deck) reverberate at a specific frequency from the shock waves. Each shock wave can also cause one or more secondary shocks to a component. For example, when a torpedo explodes under water in close proximity to a side of a boat, the explosion creates an initial shock and a bubble, which travel through the water and each impact the hull of the boat. The boat's hull will then absorb at least some of the energy from the shock wave and the bubble, and rock side to side while reverberating at a particular frequency. If the explosion is great enough, the wave of energy can even blast a hole through the hull and/or the bubble can physically lift the hull of the boat out of the water, only to have it crash down into the water and break. Regardless of whether the hull withstands the initial shock wave and bubble, each reverberation can create its own mini-shock that can causes damage to equipment and injury to people on the boat. In addition, the reverberations can act collectively at a given frequency and cause even more damage. Eventually, the energy of the shock waves dissipates and can no longer be felt. A number of factors can influence how long it takes for the shock waves' energy to dissipate, many of which need to be considered when preparing to shock test the target.
Shock tests in many ways are controlled chaos, especially the heavy weight, high explosive tests that are currently conducted. Factors, such as the positioning of the target, power of the shock, direction of the shock and reverberation of the barge, are controlled and calculated to achieve a specific objective. Accordingly, a single target or type of target may have to be tested a number of times. Each explosive shock test can cost tens of thousands of dollars, but such tests are required nonetheless by the U.S. military.